APP and Alzheimer disease: Familial AD accounts for 5%∼10% of AD patients, where inherited autosomal dominant mutations in three genes have been considered as the primary causes of familial AD: these include mutations in the genes encoding β-amyloid precursor protein (APP) and presenilins (PS1 and PS2; Goate et al., 1991; Levy-Lahad et al., 1995; Sherrington et al., 1995).